The object of the invention is a method of obtaining fresh egg products, whites, yolks or whole eggs, with a long shelf life after heat treatment, and a device implementing this method.
Methods intended for increasing the time for which egg products can be kept are already known, using heat treatment, notably pasteurising.
Numerous methods have been developed for limiting the risks of deterioration of products due to pasteurisation.
The document WO 97/10 718 describes a method of treating a liquid product based on egg, consisting essentially of white of egg and/or egg yolk. The product is subjected to a pasteurisation process with two temperature levels.
The document WO 96/38 045 describes a method of producing liquid egg with a long storage life at room temperature. The method comprises a step of heating by applying an AC electric current at high frequency, and then a cooling, and then once again a heating by the application of a high frequency AC current.
The document EP A 482 228 describes a method using a turbulent flow at high temperature (below 160xc2x0 F.) for less than one minute and then followed by an immediate rapid cooling (25 to 40xc2x0 F.)
These methods entail complex heat treatments and in spite of everything present risks of deterioration of the products.
The document FR A 2 720 602 describes a method of pasteurising liquid food products based on eggs. The liquid egg represents a small proportion, between 15 and 55% of the weight of the mixture. The pasteurisation takes place between 65 and 70xc2x0 C.
The document FR A 2 750 574 describes a method of treating liquid egg whites obtained after breaking a fresh egg including a step of substantially continuous and slow heating up to a maintenance temperature. The method comprises the following steps:
breaking the fresh eggs and separating the constituents, at a temperature of between 0 and 18xc2x0 C.;
a slow rise in temperature of the liquid egg white in a vessel with a heat exchanger, over a period of between 30 and 240 minutes, up to the maintenance temperature of between 40 and 48xc2x0 C., and preferably between 42 and 45xc2x0 C.;
maintaining the maintenance temperature at this level for one to five days, the product being packaged in air-tight receptacles.
However, this method does not concern liquid egg yolks nor whole eggs.
Other methods, using radiation, have been envisaged for preventing thermal degradation.
For example, the document WO 96/39 876 describes a method using electric fields, the document WO 95/26 636 describes a method using radio waves, the document EP-A-497 099 describes a method using alternating electromagnetic fields.
Another type of method consists of using additives.
The document FR A 2 751 181 uses bacteriologically stabilised markers, the document WO 96/32 019 uses an edible plastic covering which surrounds the eggs. The document EP A 663 151 describes a method using an acidic fermented starchy composition. However, the use of additives interferes with the obtaining of natural products.
Moreover, the use of radiation or additives is not always well perceived by consumers.
Thus a simple method is sought, making it possible to mitigate the drawbacks of the previous techniques, and to obtain liquid egg products with a long shelf life, egg white, egg yolk or whole egg, very similar to the original products, and able to be stored at room temperature for several months, typically three to six months.
The object of the invention, according to a first aspect, is a method of obtaining liquid egg products with a long shelf life, comprising heat treatment after breaking the fresh eggs and separating the components at a temperature of between 0 and 25xc2x0 C. The method comprises the steps of:
selecting at least one of the liquid fractions (9, 10, 11) to be treated obtained after breaking the eggs: egg whites (9), egg yolks (10), whole egg (11);
cold storage at a temperature below 20xc2x0 C., preferably 4xc2x0 C., for a period of less than three days, and preferably one day;
clarification or homogenisation in order to eliminate residual impurities, and bursting the fraction or fractions (9, 10, 11) into small particles, the temperature being below 20xc2x0 C.;
rapid heating of the fraction or fractions (9, 10, 11) substantially immediately or in a few minutes, up to a maintenance temperature of between approximately 40 and 55xc2x0 C. for the whites fraction (9), and preferably 45xc2x0 C., between 50 and 66xc2x0 C. for the yolk fraction (10), and preferably 55xc2x0 C., and between 50 and 66xc2x0 C. for the whole egg fraction (11), and preferably 55xc2x0 C.;
maintenance at the maintenance temperature, with degassing by slow stirring, of the fraction or fractions (9, 10, 11) for a period of between approximately 30 minutes and 4 days;
cooling to the storage temperature, below 25xc2x0 C.;
the storage life being at least three months without the incorporation of additives.
According to one embodiment, the fraction or fractions are filtered after breaking the eggs and before the cold storage.
After the cooling step which follows the temperature maintenance step, the fraction or fractions are packed in airtight packages for storage for approximately three to six months.
According to one embodiment, the cooling after the temperature maintenance step takes place in a closed loop.
According to a variant embodiment, the fractions are processed substantially simultaneously during the refrigeration storage step and the step of heating to the maintenance temperature.
According to another variant embodiment, the selected fractions are processed in alternation, successively for each step of the method.
According to one embodiment, between the step of heating to the maintenance temperature and the temperature maintenance step, the fraction or fractions undergo an additional concentration step, for example by ultrafiltration, so as to obtain an increase in the dry extract in the fractions.
The fractions are maintained at a maintenance temperature, from 40 to 55xc2x0 C. for the whites, from 50 to 66xc2x0 C. for the whole egg, with additives added such as sugar or salt before being cooled during the cooling step.
According to a second aspect, the object of the invention is a device implementing the method according to the invention. This comprises means of breaking and separating the eggs into white, yolk or whole egg fractions, means of filtering these fractions and means of cooling the filtered fractions.
The device comprises means for storing cold, typically between 0 and 4xc2x0 C., such as buffer tanks.
According to a variant embodiment, the cooling means are plate exchangers, tubular exchangers or the like, distinct from the storage means.
According to another variant, the cooling means are integrated into the double jacket buffer tank storage means.
The device comprises means of pumping the fractions refrigerated by the cooling means, into homogenisation means such as a high pressure pump and/or into washing means, the homogenisation means and the washing means enabling the fractions to burst before heating to the maintenance temperature.
The device comprises means for rapid heating above 40xc2x0 C., up to a temperature close to the maintenance temperature.
According to one embodiment, the heating means are plate exchangers.
The device comprises hot-storage means such as hot double jacket process tanks, means of monitoring and controlling the temperature in the process tanks for maintaining the fractions at the maintenance temperature, and slow stirring means for facilitating the degassing of the fractions in the process tanks.
The process tanks and buffer tanks have a capacity of between 1000 and 20,000 litres, and preferably between 5000 and 10,000 litres.
The device comprises means of cooling after the step of maintaining at the maintenance temperature, which allows cooling, in a loop, of the fractions in process tanks without the incorporation of air.
According to a variant, the device comprises means of concentration, for example by ultrafiltration, and means of drying the concentrated fractions.
It comprises means for the separate packaging of the fractions after the cooling step.